Why is Prakat day only celebrated for god Kabir ?

The proofs are available in all Holy Vedas and the scriptures that God Kabir is the father and creator of all. Others God's are stuck in the cycle of birth and death. God Kabir is free from birth and death cycle and is Indestructible.

Lord Kabir himself appears on the earth and doesn't take birth from a mother.
In the year 1398, Vikram Era 1455, in the month of jyestha, on a full moon day, at the time of Braham muhurt appeared in the form of an infant on a lotus flower in the lahartara pond.

It is clearly mentioned in Rigveda Mandal 9, Sukt 96, Mantra 17, that the almighty god himself appears on the earth to propagate his true spiritual knowledge, tatvagyan.
God kabir comes from satlok with body but his body is not made of five elements and flash and bones. It is made up of only one element that is of mass divine light and it is indestructible. God Kabir goes back to his eternal lok with body.

Saheb hokar utre, beta Kisi Ka Nahin, Jo beta hokar utre, wo saheb Kisi Ka naahi
Na mera Janm Na garbh Basera, Balak Ban dikhlaya, Kashi Nagar Jal Kamal par dear, tahan julahe ne paya.

Asthanand Rishi witnessed Lord Kabir's appearance on a lotus flower on lahartara pond.

Lord Kabir appeared on a lotus flower And Rishi Asthanand was meditating beside the pond. He saw extremely bright divine light and get contracted at the corner of the pond. He saw the effulgence of Lord Kabir who descended from satlok along with his body.

Maat Pita Mere kuch naahi na mere ghar dasi, julahe ka Sutt aan kahaya Jagat kare meri hansi

Ram, Krishna, Buddha, Mahavira and other avatars are not imperishable they take birth and die.
Only Kabir Parmeshwar ji is indestructible, free from birth and death, so manifest day is celebrated, not his birth anniversary.

Gareeb na main janmoon na maroon, jyon aaun tyon jaaun।
Gareebdas Satguru bhed se, lakho hamaara dhaanv ।।

Kabir Sahib himself has said in his speech that he himself came from Satlok and appeared in Kashi and he was not born from the parents.
Hum hain satlok ke waasi, Das kahaaye prakat bhaye kaashi।
Nahin baap na maata jaaye, avigat Gati se hum chal aaye